fonts: Add support for WOFF2 and properly load web fonts from @imports (#31879)

This change also makes two fixes that are necessary to get WOFF2 fonts
working:

1. It adds support for loading web fonts from stylesheets included via
   @import rules.
2. It ensure that when web fonts are loaded synchronusly they invalidate
   the font cache. This led to incorrect font rendering when running
   tests before.

Fixes #31598.

components/script/stylesheet_loader.rs

@@ -186,6 +186,10 @@ impl FetchResponseListener for StylesheetContext {
                         Some(&loader),
                         win.css_error_reporter(),
                     );
+
+                    // Layout knows about this stylesheet, because Stylo added it to the Stylist,
+                    // but Layout doesn't know about any new web fonts that it contains.
+                    document.load_web_fonts_from_stylesheet(stylesheet.clone());
                 },
             }